Dampers and shock-absorbers are known which use a hydraulic fluid as the working medium to create damping forces to control or minimize shock and/or vibration. Typically, the damping forces are generated by a pressures resisting movement between operative components of the damper or shock absorber. One class of these devices includes magnetorheological (MR) fluid devices. MR devices may be of the xe2x80x9crotary-actingxe2x80x9d or xe2x80x9clinear-actingxe2x80x9d variety. Known MR devices include linear dampers, rotary brakes and rotary clutches. Each MR device employs a Magnetorheological (MR) fluid comprised of soft-magnetic particles dispersed within a liquid carrier. Typical particles include carbonyl iron, and the like, having various shapes, but which are preferably spherical and have mean diameters of between about 0.1 xcexcm to about 500 xcexcm. The carrier fluids include low viscosity hydraulic oils, and the like. In operation, these MR fluids exhibit a thickening behavior (a rheology change) upon being exposed to a magnetic field. The higher the magnetic field strength exposed to the fluid, the higher the damping/restraining force or torque that can be achieved within the MR device.
MR fluid devices are disclosed in U.S. Pat. No. 5,816,372 entitled xe2x80x9cMagnetorheological Fluid Devices And Process Of Controlling Force In Exercise Equipment Utilizing Samexe2x80x9d, U.S. Pat. No. 5,711,746 entitled xe2x80x9cPortable Controllable Fluid Rehabilitation Devicesxe2x80x9d, U.S. Pat. No. 5,842,547 entitled xe2x80x9cControllable Brakexe2x80x9d, U.S. patent application Ser. No. 08/674,179 now U.S. Pat. No. 5,878,871 entitled xe2x80x9cControllable Vibration Apparatusxe2x80x9d and U.S. Pat. Nos. 5,547,049, 5,492,312, 5,398,917, 5,284,330, and 5,277,281, all of which are commonly assigned to the assignee of the present invention.
Known MR devices advantageously can provide controllable forces or torques, as the case may be, but, as currently designed, such devices are comparatively expensive to manufacture. These devices typically include a housing or chamber that contains a quantity magnetically controllable fluid, with a movable member, a piston or rotor, mounted for movement through the fluid in the housing. The housing and the movable member both include a magnetically permeable pole piece. A magnetic field generator produces a magnetic field across both pole pieces for directing the magnetic flux to desired regions of the controllable fluid. Such devices require precisely toleranced components, expensive seals, expensive bearings, and relatively large volumes of magnetically controllable fluid. The costs associated with such devices may be prohibitive to their use in certain applications, for example, washing machines and home exercise devices. Therefore, there is a long felt, and unmet, need for a simple and cost effective MR fluid device for providing variable forces and/or torques.
The present invention is a continuation-in-part of U.S. application Ser. No. 08/959,775 to J. David Carlson entitled xe2x80x9cCONTROLLABLE MEDIUM DEVICE AND APPARATUS UTILIZING SAMExe2x80x9d filed Oct. 29, 1997.
The present invention provides a controllable medium device which uses a vastly reduced quantity of controllable rheological medium as compared to prior art devices, and which eliminates the need for expensive seals, bearings, and precisely toleranced components. As a result, the cost to manufacture such devices is dramatically reduced.
According to the invention, a small amount of controllable medium, preferably in fluid form, is entirely contained in a working space between relatively movable members subjected to the magnetic field by a fluid-retaining means, for example, an absorbent matrix (preferably an open cell foam or the like) or a wicking member. The inventor herein discovered that an absorbent member can hold a sufficient amount of fluid to produce a significant rheological effect between a first pole member and a relatively movable second pole member. The invention may be incorporated in various physical embodiments such as linear dampers, rotary dampers such as brakes, mountings, pneumatic devices and applications therefor.
In particular, the present invention is a magnetorheological medium device which comprises first and second members coupled for relative movement and having a working space therebetween, means for producing a magnetic field that acts on the first and second members and the working space and a field controllable medium contained substantially entirely in the working space.
A working space is provided by spacing the first and second members using structural supporting means. In a piston and cylinder device, for example, a working space is provided by selecting a piston head to have an outer dimension that is smaller than an inner dimension of the cylinder by a predetermined amount. The difference in size provides the working space when the piston head is assembled in the cylinder. In a piston and cylinder device, the structural support to maintain the spacing may conveniently be provided by a fluid retaining material surrounding and preferably fixed to the piston head. In a disk brake device, the working space is provided by mounting the rotor and caliper yoke in such a way as to space apart the surface of the rotor and the inner surfaces of the calipers. In other devices, spacing means for maintaining a constant gap dimension of the working space are positioned at a first and second end of the matrix structure. Preferably, the spacing means comprises at least one disc and may be integral with a first member.
According to a preferred embodiment of the invention, a controllable fluid is contained in the working space by a material providing an absorbent matrix disposed in the working space. Absorbent matrix is used here to indicate a material that has the ability to pick up and hold a fluid by wicking or capillary action. In a particularly preferred embodiment, the absorbent matrix is a sponge-like material, for example, an open-celled or partly open-celled foam. Polyurethane foam and rubber foam are examples of particularly suitable materials. Foams made of other materials are also suitable, and examples include silicone rubber, polyamide, viton rubber, neoprene, Ioner rubber, melamine, a polyimide high temperature foam and metal foams.
An absorbent matrix can also be formed of other material structures, such as an unwoven material (e.g. a mineral wool), or a felt, for example, Nomex brand aramid fiber felt or a compressed carbon fiber felt. In addition, a woven fabric could be used, made from materials such as Kevlar brand fiber, graphite, silica, Nomex brand aramid fiber, polybenzimadazole, Teflon brand fiber and Gore-Tex brand fiber. Alternatively, a mesh material, such as a metal mesh, could be used.
Other structures that can contain a fluid, for example, brushes, flocked surface materials, wipers, and gaskets are also suitable.
The absorbent matrix need not entirely fill the working space, as long as the field controllable medium is contained in the working space. Thus, the absorbent matrix may be formed as a structure having a plurality of cavities, such as a honeycomb or other network structure, to contain the medium in the working space.
By containing an effective amount of controllable medium only in the working space of the device, no expensive seals are needed to contain the controllable medium as in the prior art.
According to another aspect, the invention comprises an apparatus, such as a controllable damper, having a transmission that converts relative linear motion between a first and second component into rotational motion of the second member. Further, the transmission may increase the relative motion and speed between the first and second members. Such transmission means preferably causes a mechanical amplification which multiplies the force produced by the apparatus by a predetermined factor.
In particular, the apparatus comprises a disc rotably mounted to a housing, a pole unit mounted stationarily relative to the housing, and a field generator. The disc is coupled to the first component (e.g., including a rod or rack) by means of a friction drive or pinion gear. The working space between the rotor disc and pole unit is filled by a fluid retaining matrix structure. This embodiment of the invention substantially reduces the amount of high-permeability steel required in the device for any given force capacity. Except for the electromagnetic coil and matrix filled structure retaining the field responsive medium (e.g., magnetorheological fluid), all other components may be made from low permeability, non-magnetic materials such as plastic or aluminum.
According to another aspect, the invention is an apparatus, comprising: a first component, a second component including; a housing, a first member mounted stationarily relative to the housing, and a second member spaced from the first member to form a working space therebetween, the second member rotatable relative to the first member, a matrix structure disposed in the working space, a field responsive medium retained in the matrix structure, and a field generator for generating a flux in said members thereby producing a field in the working space to change the rheology of said medium and resultantly produce a resistance to relative motion between said members, and a transmission converting linear motion of the first component to rotary motion of the second member.
According to another aspect, the invention comprises a first component, a second component including a first member, a second member spaced from the first member to form a working space therebetween, means for mounting the second member such that the second member may rotate relative to the first member, a matrix disposed in the working space, a field responsive medium retained in the matrix structure, and means for producing a magnetic field in the working space to change the rheology of the medium and resultantly produce a resistance to relative motion between the members, and means converting linear motion of the first component to rotary motion of the second member.
According to another aspect, the invention is an apparatus, comprising: a first component, and a second component that is moveable relative to the first component, the second component including; a housing, a first member mounted stationary in the housing, a second member spaced from the first member to form a working space therebetween, means for rotatably mounting the second member in the housing such that the second member may rotate relative to the first member, means for retaining a field responsive medium in the working space, and means for producing a field in the working space to change a rheology of the medium and resultantly produce a resistance to relative motion between said members, and a transmission converting linear motion of the first component to rotary motion of the second member.
It is another advantage of the invention that the amount of controllable medium needed to accomplish the rheology-based resistance effect is dramatically reduced to only the amount contained in the working space.
Another advantage of the invention, is providing a linear damper that requires no seals or bearings.
Another advantage of the invention, is providing a linear damper that doesn""t require precisely toleranced components, i.e., non-ground piston rods and loosely toleranced outer member tubes and pistons.
According to the invention, means for generating a field in the first and second member and the working space is mounted to either of the first or second members in proximity with the working space. For example, in a piston/cylinder damper, the generating means can be at least one coil circumferentially wrapped on the piston head. In a rotary damper, the generating means can be at least one coil mounted to a yoke having arms between which the rotor turns.
A damping device in accordance with the invention can be incorporated in a number of apparatuses where it previously was cost-prohibitive to use controllable dampers. For example, the dampers of the invention can be used in washing machines to control vibration during various cycles. A resistance device of the invention can also be incorporated in exercise devices, such as bicycles, step machines, and treadmills to provide variable resistance.
The above-mentioned and further features, advantages and characteristics of the present invention will become apparent from the accompanying descriptions of the preferred embodiments and attached drawings.